1. First, read the ingredients and instructions and get acquainted with the recipe. Measure out all your ingredients. Place the sugar, cornstarch,cocoa powder and salt in a heavy duty saucepan . Whisk the ingredients together. Take the butter and vanilla and place it near the stove so it's measured out and ready when you need it.
2. After whisking the ingredients together you may see clumps in the mixture, they are cocoa clumps. Take the back of a kitchen tablespoon and press the large clumps out.
3. With a whisk in one had, slowly pour the milk into the pan while whisking.
4. Place the pan on a burner turned to low heat and whisk the mixture slowly. Why low heat? Your pudding has to thicken SLOWLY. This is where you need a little patience. It's going to take about 10 minutes on low heat for the pudding to start to thicken and come up to a boil while you whisk. Turning the heat up to speed the process won't help. You may run the risk of burning it or it may boil quickly but the pudding will not have thickened. What you'll be left with is hot chocolate soup. If the pudding hasn't thickened and come up to a boil in the saucepan, it won't set up in the refrigerator either. I can't tell you how many times I've read comments on recipes where someone said..."It came to a boil but never set up in the refrigerator". Why would that happen? The heat was up to high, the mixture boiled , before it thickened. It will always thicken first, then boil. Patience Grasshopper, it's a virtue.
5. When the pudding does thicken, it will happen fast and all at once. With in seconds it will start to boil. Large bubbles will come to the surface and erupt like little volcanoes. Whisk for one more minute.
6. Your pudding should be thick enough to coat the back of a spoon without seeing the metal on the spoon through the pudding. Take the pudding off the burner and add the butter and vanilla , whisk to incorporated it into the pudding. Pour the pudding into 4 dessert cups, a graham cracker crust or a pie crust depending on how you want to serve it. Press plastic wrap onto the pudding surface so it actually touches the surface of the pudding. This prevents a "skin" from forming on the top of the pudding when it cools. Refrigerate for about 2 hours until cooled. Top with whipping cream if desired and serve.